The aim of this study was genetic parameter estimation in Iranian Brown Swiss crossbred dairy
population. The performance of Brown Swiss crossbred cattle in Iran was considered across years 1991-2003.
Variance component were estimated using animal model (single trait) and Derivative-free restricted Maximum
Likelihood method for different traits. The estimation of the heritability for milk yield, fat yield, and fat
percentage and milk days were 0.24, 0.163, 0.175 and 0.334, respectively for single models. Repeatability
estimation for mentioned traits was 0.41, 0.31, 0.18 and 0.334. The result showed that the additive genetic
variance share in milk yield and milk day’s traits and permanent environmental variance in milk and fat yield
are high.